Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The present invention may find applicability in all such applications, although the description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227 (“the '227 patent”), which is incorporated herein by reference in its entirety.
Spinal cord stimulation is a well-accepted clinical method for reducing pain in certain populations of patients. As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible case 30 formed of titanium for example. The case 30 usually holds the circuitry and power source or battery necessary for the IPG to function. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112, 114, coupled to each electrode. The signal wires 112 and 114 are connected to the IPG 100 by way of an interface 115, which may be any suitable device that allows the leads 102 and 104 (or a lead extension, not shown) to be removably connected to the IPG 100. Interface 115 may comprise, for example, an electromechanical connector arrangement including lead connectors 38a and 38b configured to mate with corresponding connectors 119a and 119b on the leads 102 and 104. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The electrode array 110 is typically implanted along the dura of the spinal cord, and the IPG 100 generates electrical pulses that are delivered through the electrodes 106 to the nerve fibers within the spinal column. The IPG 100 itself is then typically implanted somewhat distantly in the buttocks of the patient.
As shown in FIG. 2, an IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors, mounted to the PCB 16. Ultimately, the electronic circuitry performs a therapeutic function, such as neurostimulation. A feedthrough assembly 24 routes the various electrode signals from the electronic substrate assembly 14 to the lead connectors 38a, 38b, which are in turn coupled to the leads 102 and 104 (see FIGS. 1A and 1B). The IPG 100 further comprises a header connector 36, which among other things houses the lead connectors 38a, 38b. The IPG 100 can further include a telemetry antenna or coil 96 (FIG. 1A) mounted within the header connector 36 for transmission and receipt of data to and from an external device such as a hand-held or clinician programmer (not shown). As noted earlier, the IPG 100 usually also includes a power source 26, usually a rechargeable battery 26. The power source 26 can be recharged transcutaneously by an external charger 12. Specifically, when active during a charging session, the external charger 12 energizes its charging coil 17, which in turn induces a current in the charging coil 18 in the IPG 100. This induced current is rectified and ultimately used to charge the power source 26 through the patient's flesh 25.
Further details concerning the structure and function of typical IPGs and IPG systems are disclosed in U.S. patent application Ser. No. 11/305,898, filed Dec. 14, 2005, which is incorporated herein by reference.
A traditional architecture 50 for the circuitry inside of an IPG 100 is shown in FIG. 3. As one skilled in the art will appreciate, FIG. 3 depicts the IPG 100's circuitry at a relatively high level sufficient to understand the points this disclosure makes. The architecture 50 contains basic circuit blocks for executing various electrical functions in the IPG 100. For example, telemetry circuit 62 is coupled to coil 96, and operates to send and receive data to and from an external controller (not shown). Charging and battery protection circuitry 64 is similarly coupled to charging coil 18, and intervenes between the power source 26 and the rest of the circuitry. Both of these circuits 62 and 64 are coupled to a microcontroller 60, which as can be noticed is central to the design of the architecture 50. Programs and data needed by the microcontroller 60 upon power up are stored in a memory 66, preferably a serial nonvolatile memory, which is coupled to the microcontroller 60 by a serial interface 67.
Circuitry involved in providing a predictable therapy of stimulation is provided by a digital integrated circuit (IC) 70 and an analog IC 80. In one application, the digital IC 70 contains stimulation control logic, such as the various timers that are used by the IPG's timing channels to provide a stimulation pulse train with a particular timing. The analog IC 80 receives data from the digital IC 70 via a serial link, where such data is converted to analog signals by a digital-to-analog converter (DAC) 82, which in turn ultimately provides the stimulus to the electrodes (E1 . . . EN). Additionally, an analog-to-digital (A/D) converter 74 is used to inform the microcontroller 60 of various analog voltages being produced or monitored on the analog IC 80, such as various reference voltages, the stimulation compliance voltage, etc., and within the charging 64 and telemetry 62 blocks. Although shown as integrated with the microcontroller 60, the A/D converter 74 could also be a discrete component outside of the microcontroller 60.
In one embodiment, the microcontroller 60, the digital IC 70, and the analog IC 80 comprise discrete ICs each comprising one of the components 20 on the IPG's printed circuit board 16 (see FIG. 1). Other functional blocks in the architecture 50 might comprise other components 20, which might not be integrated but rather formed at least in part of discrete components.
Having briefly described the functional blocks in architecture 50, it should be noted that it is not important to the present disclosure to understand the detailed workings of those blocks. (The reader can consult the above-incorporated '898 application should a greater knowledge of each of the functional blocks be desired). Instead, what is important to understand is the manner in which the functional blocks are interconnected. As one skilled in the art will understand, central to the operation of architecture 50 is the microcontroller 60, which ultimately receives and issues all commands from and to the other blocks. Furthermore, it can be noticed that the various interconnections between the blocks vary in type and complexity, with some connections being serial in nature, and others comprising single data lines or comprising data digital busses. Moreover, some of the blocks lack direct connections with other blocks, and hence must communicate through intermediary blocks. For example, the microcontroller 60 must, at least in part, communicate with the analog IC 80 through the digital IC 70.
Such inter-connectivity adds to the expense of the IPG 100 and its complexity. Moreover, it also makes it difficult to adapt a particular architecture to desired changes and/or newer IPG revisions. For example, the changing of one of the functional blocks may require significant corresponding changes in other functional blocks, making upgrades or revisions expensive.
Additionally, space within an IPG 100 is limited, because IPGs are preferably as small as possible to make the implant as unobtrusive as possible for the patient. In this regard, the architecture 50 of FIG. 3 is further problematic because of its requirement of separate IC used for the microcontroller 60, the digital IC 70, and the analog IC 80 (and possibly other components). Having numerous components generally negatively impacts the reliability of the circuit, and increases power consumption, generally a big concern for a power-limited IPG.
This disclosure presents a solution to this problem in the art of implantable medical devices via an improved IPG architecture.